The analog-to-digital converter unit in a programmable logic controller system, which is disclosed in Patent Literature 1, comprises an MPU (Micro Processing Unit), an arithmetic unit, a bus control unit and an analog-to-digital converter device. Analog data inputted to the analog-to-digital converter device from outside the analog-to-digital converter unit are converted into digital data. The converted digital data are inputted to the arithmetic unit and arithmetic processing is performed thereon. The digital data subjected to arithmetic processing are transferred to the bus control unit by the MPU and transferred to a CPU (Central Processing Unit) from the bus control unit via a base unit.
The marketplace demands that data conversion and response in the programmable logic controller system be made faster in processing, and to this end, the processing in the analog-to-digital converter unit needs to be made faster. An object to be made faster in the internal processing of the analog-to-digital converter unit is the time required for data conversion by the analog-to-digital converter device, the operation time in the arithmetic unit, or the time required for data transfer by the MPU.